High conductivity lightweight third rail for electric railways

ABSTRACT

A third rail is provided having the outer cross-sectional configuration of a conventional solid steel third rail but made hollow and composed of aluminum for high conductivity and lightweight with a stainless steel cap for abrasion resistance. Although the third rail is hollow it has sufficient conductivity and current carrying capacity to supply much heavier trains than conventional steel rails. The surface of the rail on which the steel cap is fastened is slotted but the slot is substantially closed by employing the cap to stress the material of the hollow rail to produce a force pressing the steel cap against the adjacent rail surface to achieve low contact resistance.

United States Patent 1 1 Corl et al.

[ 1 May 27, 1975 [75] Inventors: James A. Cori, San Carlos; Ronald J. Kilburg, Belmont, both of Calif.

[73] Assignee: The Rucker Company, Oakland,

Calif.

[22] Filed: Apr. 27, 1973 [21] Appl. No.: 355,050

[52] U.S. Cl 191/29; 238/143 [51] Int. Cl B60m l/30 [58] Field of Search 238/143, 148, 134; 191/22,

Primary E.ramincrLloyd L. King Assistant Examiner-Richard A. Bertsch Attorney, Agent, or Firm-Knobbe, Martens, Olson, Hubbard & Bear [57] ABSTRACT A third rail is provided having the outer crosssectional configuration of a conventional solid steel third rail but made hollow and composed of aluminum for high conductivity and lightweight with a stainless steel cap for abrasion resistance. Although the third rail is hollow it has sufficient conductivity and current carrying capacity to supply much heavier trains than conventional steel rails. The surface of the rail on which the steel cap is fastened is slotted but the slot is substantially closed by employing the cap to stress the material of the hollow rail to produce a force pressing the steel cap against the adjacent rail surface to achieve low contact resistance.

10 Claims, 3 Drawing Figures HIGH CONDUCTIVITY LIGHTWEIGHT THIRD RAIL FOR ELECTRIC RAILWAYS SUMMARY OF THE INVENTION Extruded aluminum or high conductivity light metal alloy is utilized substantially in the form of a hollow box channel with an open slot in the top, somewhat curved convex surface. A stainless steel cap is applied to this surface to enable a conventional conductor shoe to ride on the rail without wearing the light metal surface. The cap is in the form of a U-channel or clip with sides extending downward and bent inwardly to fit grooves in the sides of the hollow rail to retain the cap on the rail. The dimensions are such that the slot in the top of the rail is forced substanially shut so that the cap is in tension and the material of the rail is subjected to bending stress so as to pull the lower surface of the cap down against the upper convex surface of the top side of the rail to provide close physicalcontact and low electrical contact resistance. In addition, electrically conductive grease may be introduced upon the surface to avoid the formation of oxides which might produce electrical resistance.

A better understanding of the invention will be afforded by the following detailed description considered in conjunction with the drawings.

DRAWINGS FIG. 1 of the drawings is a cross-sectional view of an embodiment of the invention;

FIG. 2 is a fragmentary view to a reduced scale illustrating the manner in which electrical conducting joints are made between the successive lengths of the third rail; and

FIG. 3 is a diagram illustrating a method of assembly.

Like reference characters are utilized in the drawings to designate like parts.

DETAILED DESCRIPTION As illustrated in FIG. 1, a rail 11 is utilized which has the cross-section of a conventional rail such as used for third rails in electric railways, rapid transit systems and other apparatus such as which cranes wich run on tracks and have traction motors. In fact, the crosssectional outline is preferably the same as that of solid steel third rails now in use in order that the third rail in the present invention may be substituted in parts of the system without simultaneous complete replacement of all the third rails of a railway system.

However, the material of the rail 11 is selected to have a considerably higher conductivity than conventional steel rails in order that the system may be used with substantially increased electric load. The material is preferably aluminum or comparable light metal alloy having high electrical conductivity. As a result of the substantially higher electrical conductivity the rail 11 may be hollow, as shown, in a form which may be referred to for convenience as a box channel. This form also provides high strength and rigidity while further enhancing the lightness of the rail.

In order to retain adequate resistance to abrasion from the current collector shoe of a car or carriage which travels on tracks along the third rail, a cap 12 is secured to the top side 13 of the box channel 11. The cap 12 is composed ofa suitable material such as spring grade. half-hard stainless steel. for example. a stainless steel alloy known in the steel industry as grade number 301. A spring grade steel is essential in order that the cap 12 may be formed with sides 14 and 15 which toe in against sides 16 and 17 ofthe box channel 11 so that the cap 12 holds itself securely upon the top side 13 of the box channel II. In addition the box channel 11 is so formed that it has a slot 20 in the top side 13 which would have a substantial gap if the material of the box channel 11 were in unstressed condition. However. the parts are so dimensioned that the edges of the slot 20 are drawn together so as substantially to close the slot 20 as shown in the drawing. In this manner the material of the box channel 11 is also under stress. namely bending stress, so that the sides 16 and 17 tend to press outward against the sides 14 and 15 of the cap 12. Preferably the box channel 11 is so shaped that sides 16 and 17 toe outward so as to react forcefully against the inwardly toeing cap sides 14 and 15.

Preferably, to assure retention of the cap 12 upon the top side 13 of the box channel, the lower edges of the cap sides 14 and 15 are crimped to form teeth 18 and 19 fitting and preferably biting into grooves 21 and 22 in the channel sides 16 and 17. Moreover, the top surface 23 of the channel top side 13 is slightly curved so as to be slightly convex as in conventional solid steel third rails, and the cap 12 is conformably shaped so that its under surface 24 is drawn downward as the cap 12 is stretched across the channel top surface 23 by the force acting between the cap 12 and the sides of the box channel 11. This tends to force the confronting surfaces 23 and 24 together in tight physical contact with minimum electrical contact resistance.

In order to insure and preserve such low electrical contact resistance preferably a suitable material such as electrically conducting grease is applied to one or the other of the confronting surfaces before the cap and the illustrated rail are assembled so that oxidation of the confronting surfaces is prevented or retarded. In this manner the introduction of electrical resistance of oxides is avoided. A substance sold by the Aluminum Company of America under the designation Alcoa EJC-Z has been found satisfactory as an electrically conducting grease. As shown the cap 12 is relatively thin so that it introduces little resistance in spite of the higher resistivity of steel than aluminum.

As a still further assurance of retention of the cap upon the top side 13 of the box channel 11, suitable additional fastening means may be employed such as staking, plug welds or nails. Plug welds are described in US. Pat. Nos. 3,582,575, column 1, line 53; 3,602,655, column 1, line 53; and 3,399,281, column 2, line 54, and column 3, line 65 to column 4, line 19. In the embodiment illustrated in this application, inch long, 5/32 inch diameter nails 25 are utilized of the explosive driven type which pierce the sides 14 and 15 of the cap 12 and enter the sides 16 and 17 of the aluminum box channel. A cap composed of stock 5/32 inch to inch thick has been found suitable. Preferably washers 26 are provided under nail heads 27. An explosive powered tool may be employed for driving the nails 25 as illustrated in FIG. 5 of U.S. Pat. No. 3,602,655. Suitable nails are those sold as UTM Hilti by Fastening Systems of Stamford, Conn., Model No; DX lOOL or those sold under the trademark Ramset by Olin Matthiesen Chemical Co.

Starting points for fissures are avoided and good springiness under bending stress is obtained in the aluminum material by forming the box channel with grooves 30 at the junctions of the sides 16 and 17 .with the relatively flat base 10 of the box channel 11. In this case of third rails having the external dimensions of I50 pound solid steel rails, the radius of curvature of grooves 30 may be approximately 3/32 of an inch.

As shown and as in conventional rail shapes. the sides 16 and 17 have recessed portions 28 adapted to receive fish plates 29 in order that successive lengths of third rails may be joined as illustrated in FIG. 2. For this purpose preferably high tensile strength. zinc coated bolts 31 are inserted with flat washers 32 and Bellville or truncated conical washers 33. Nuts 34 of self-locking type, are employed for example, type 4 PLCS. The fish plates 29 are preferably composed of electrical grade aluminum such as used for the extrusion ll. Inserts 35 extending into the ends ofjoined rails may also be employed taking the form of accordion-spring extrusions similar to the rail-head portions of rails shown in FIG. of U.S. Pat. No. 3,602,655 but with parallel sides.

It has been found that 150 pound solid steel third rails are suitable for carrying approximately 3,000 amperes to the traction motors used in trains. These have a resistivity of from 3.78 to 4.06 microhms per foot. However, with heavier loads being carried by electric railways and more powerful traction motors being em ployed as well as heavier hoist motors on track carried cranes there is a need for rails with a current carrying capacity of 6,000 amperes with a resistivity ofonly 2.00 microhms per foot, direct-current, at 20 centigrade. This result is achieved by the rail illustrated having the external dimension of a 150 pound solid steel rail. The desired current-carrying capacity is achieved in hollow aluminum rails having a wall thickness approximately inch, where the base has a width of 4 /8 inches and the overall height is approximately 4 inches.

This avoids the necessity of providing solid copper cables for adequate current carrying capacity and to prevent excessive voltage drop. It also avoids need for bolting or scabbing aluminum bus bars to the third rails. However, the invention is not limited to use with high power electrical railways. It may also be employed in systems which continue use of smaller third rails. For example, it is useful in railroads that have 80, 85 or 100 pound rails as third rail conductors and railroads that use 3,000 ampere rails with conductivity 3.78 4.06 microhms per foot. For such railroads it will be under- .stood that aluminum rails with appropriate steel caps would be employed with external dimensions conforming in shape to solid steel rails previously used in such railroads. In such cases hollow aluminum with approximately 3/16 of an inch thick walls may be employed. Preferably the rails as shown in the drawing are aluminum extrusions of strong electrical grade such as that known in the trade as ASTM 06063-T6, e.g. The rails are initially formed with an extruded opening along the slot approximately A of an inch wide. This opening provides a faster extruded time for lower cost and it also provides, as already described, a spring action to assure good electrical contact with a stainless steel cap. The electrical distribution system with which the third rail of this application may be employed does not constitute a part of the present invention. It will be understood, however, that when such third rails are employed with railway tracks there are carriages or railway trucks which carry suitable current-collector heads such as illustrated for example in U.S. Pat. No.

3,602,655 or Des 200,167. Before assembling the cap I2 with the box channel 11 the aluminum channel 11 should have surface oxide removed from the top surface 23 and the sides. This may be accomplished by brushing as described in U.S. Pat. No. 3,602,655.

Although the invention is not limited to a particular method of assembly we prefer to assemble the composite third rail by pressing the cap 12 upon the top of the box channel ll, applying pressure transversely against the cap I2 by a pressure plate 36, which may be actuated by a hydraulic piston 37. However, the assembly is performed sequentially, beginning at one end and working toward the other.

As illustrated in FIG. 3, the cap 12 is sufficiently flexible that the left end may be pressed in place while the remainder has only partially embraced the sides of the box channel 11. Before lifting the pressure plate 36. the nails 25 with heads 27 are driven into place to secure this portion of the cap permanently. The process is carried'out step by step moving the pressure plate and rail relatively to each other until the entire cap 12 has been pressed in place and nailed;

During application of pressure to the cap 12 against the box channel 11, the cap sides 14 and 15 are forced outward to enclose the sides of the box channel 11 and force them inward. During this action the galling effect of the teeth 18 and 19 of the cap 12 upon the sides of the box channel 11 serves to scrape off particles of alu'-.

minum oxide which may have remained after the brushing operation, thereby assuring good electrical contact.

While a particular form of the invention has been illustrated and fully described, it will be obvious to those skilled in the art that various modifications and alterations may be made therein and it is intended to cover all such modifications and alterations as may fall within the scope of the invention.

What is claimed is:

1. A composite electrical conductor comprising:

a hollow rail made of lightweight electrically conductive material such as aluminum, the rail having a base, two sides integrally formed with the base and an upper wall integrally attached to the sides, the upper wall being formed in two segments which are slightly spaced from each other when the rail is in an unstressed condition; I

a U-shaped cap formed of an electricaly conductive material such as steel which wears better than aluminum, the cap being dimensioned to fit onto the upper portion of the rail and stress the rail so as to substantially close the gap between the two segments of the rail upper wall and introduce pressure between the cap and the rail to assure good electrical contact between them, the cap and the rail being sufficiently springy such that they remain under stress so as to continue good electrical contact, means forming rounded internal grooves at the junction between the sides and base of the rail which facilitate moving the walls to close the gap when the cap is snapped onto the rail; and means maintaining the cap on the rail in addition to the spring forces of the material. 5 2. A conductor bar as described in claim 1 wherein the rail base is approximately 5 inches wide, 4 inches high and has a wall thickness of approximately /s inch carrying a cap having a thickness between approximately 5/32 inch and A inch.

3. A composite electrical conductor bar including:

a hollow rail formed with a substantially closed crosssection except for an elongated gap extending lengthwise along the rail; and

a cap interference fitting over the portion of the rail having the gap and stressing the rail in the gap closing direction, the cap being formed to conform to the exterior of the rail and being formed of springy material and dimensioned so that it is under spring tension, thereby assuring good electrical contact between the cap and the rail.

4. The conductor of claim 3 wherein the cap is formed of spring grade steel and the rail is formed of a material, such as aluminum, which is a better electrical conductor than the steel cap.

5. The conductor of claim 3 wherein the rail has a supporting base, a pair of sides integrally formed with the base and a rail head integrally formed with the sides with said gap being formed in the rail head, and wherein said cap fits over the rail head and onto the rail sides to form a contact surface for the rail.

6. The conductor of claim 5 wherein the sides of the rail when unstressed toe outwardly with respect to a line perpendicular to the rail base, and the sides of the cap toe inwardly so as to urge the sides of the rail into position perpendicular to the base of the rail.

7. The conductor of claim 5 wherein the rail head has a slightly convex surface whereby the force acting between the cap and the rail draws the cap against said surface for close physical contact and low electrical contact resistance.

8. The conductor of claim 5 wherein the sides of the rail are formed with grooves spaced from the rail head and the cap is formed with crimped edges fitting into said grooves, the cap being sufficiently springy such that it can be pre-formed and then pressed directly onto the rail head.

9. The conductor of claim 5 including fastening means extending through the sides of the cap and into the sides of the rail to further secure the cap to the rail.

10. The conductor of claim 5 including means at the junctions between the base and the sides which cause the sides to pivot or bend around these junctions when the cap is snapped onto the rail. 

1. A composite electrical conductor comprising: a hollow rail made of lightweight electrically conductive material such as aluminum, the rail having a base, two sides integrally formed with the base and an upper wall integrally attached to the sides, the upper wall being formed in two segments which are slightly spaced from each other when the rail is in an unstressed condition; a U-shaped cap formed of an electricaly conductive material such as steel which wears better than aluminum, the cap being dimensioned to fit onto the upper portion of the rail and stress the rail so as to substantially close the gap between the two segments of the rail upper wall and introduce pressure between the cap and the rail to assure good electrical contact between them, the cap and the rail being sufficiently springy such that they remain under stress so as to continue good electrical contact, means forming rounded internal grooves at the junction between the sides and base of the rail which facilitate moving the walls to close the gap when the cap is snapped onto the rail; and means maintaining the cap on the rail in addition to the spring forces of the material.
 2. A conductor bar as described in claim 1 wherein the rail base is approximately 5 inches wide, 4 inches high and has a wall thickness of approximately 3/8 inch carrying a cap having a thickness between approximately 5/32 inch and inch.
 3. A composite electrical conductor bar including: a hollow rail formed with a substantially closed cross-section except for an elongated gap extending lengthwise along the rail; and a cap interference fitting over the portion of the rail having the gap and stressing the rail in the gap closing direction, the cap being formed to conform to the exterior of the rail and being formed of springy material and dimensioned so that it is under spring tension, thereby assuring good electrical contact between the cap and the rail.
 4. The conductor of claim 3 wherein the cap is formed of spring grade steel and the rail is formed of a material, such as aluminum, which is a better electrical conductor than the steel cap.
 5. The conductor of claim 3 wherein the rail has a supporting base, a pair of sides integrally formed with the base and a rail head integrally formed with the sides with said gap being formed in the rail head, and wherein said cap fits over the rail head and onto the rail sides to form a contact surface for the rail.
 6. The conductor of claim 5 wherein the sides of the rail when unstressed toe outwardly with respect to a line perpendicular to the rail base, and the sides of the cap toe inwardly so as to urge the sides of the rail into position perpendicular to the base of the rail.
 7. The conductor of claim 5 wherein the rail head has a slightly convex surface whereby the force acting between the cap and the rail draws the cap against said surface for close physical contact and low electrical contact resistance.
 8. The conductor of claim 5 wherein the sides of the rail are formed with grooves spaced from the rail head and the cap is formed with crimped edges fitting into said grooves, the cap being sufficiently springy such that it can be pre-formed and then pressed directly onto the rail head.
 9. The conductor of claim 5 including fastening means extending through the sides of the cap and into the sides of the rail to further secure the cap to the rail.
 10. The conductor of claim 5 including means at the junctions between the base and the sides which cause the sides to pivot or bend around these junctions when the cap is snapped onto the rail. 